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Only two species of bean are popular in cultivation in Europe, also in Poland: common bean (Phaseolus vulgaris L.) and runner bean (Phaseolus coccineus L.).

In bean cultivation for dry seeds there is a possibility of obtaining additional yield, namely stripped pods, the pericarp of bean. The pods of bean were used already in 19th century as a diuretic medicine. At present, the pericarp of bean has the major significance as antidiabetic agent and in the treatment of renal duct disorders.

The pericarp of bean Phaseoli pericarpium syn. Fructus phaseoli sine semine is a pharmacopoeic material described in Polish Pharmacopoeia VI [5]. This material should come from white-flowered cultivars of Phaseolus vulgaris L. and should contain not less than 0.01% (0.1 mgˇg-1) of phenolic acids in convertion to caffeic accid. There is no information available about the content and chemical composition of the pericarp of Phaseolus coccineus L., the species of bean which is also widespread in cultivation [11]. Only two sources suggest about the possibility of using the pericarp of runner bean: Volák and Stodola [16] and Cybulska [3]. The research Łabuda at al. [12] indicate that the pericarp of runner bean (Phaseolus coccineus L.) contains valuable biologically active substances.

Therefore the purpose of the research done in years 1999-2000 was the determination of the content and identification of free phenolic acids in bean pericarp Phaseolus vulgaris L. and Phaseolus coccineus L.

In order to compare the possibilities of using the pericarp of runner bean and common bean as herbal material, scrub cultivars were taken into consideration: Eureka and Blanka (runner bean) and Aura, Igołomska and Longina (common bean).

HPLC analyses were done with the use of liquid chromatograph, type LaChrom, with detector DAD L-7455, thermostat L-7360, pump L-7100, degaser L-7612 and dosing loop 20 ľl. The analyses were done in the reverse phases system using steel column LiChrospher 100 RP-18 250-4; the mobile phase was the solution of methanol + water (25+75 v/v) with of 1% acetic acid, at the speed of flow of 0.8 ml/min and the temperature of 25°C. The identification of compounds was done on the basis of comparison of their retention time and spectra with the retention time and the spectra of the standard [14].

The widespread chemical, pharmacological and clinical research carried out throughout the world and concerning the usefulness of herbs and vegetal medicines in therapy explicitly show that the agents and methods used in traditional medicine should not be rejected [6].

As it results from the literature, there has been a distinct development of the knowledge of the chemism of plant materials recently. However, the research on Phaseoli pericarpium is fragmentary and do not allow to elaborate the proper evaluation of this material. The drawback is also that there is a lack of proper normalization of antidiabetic mixtures, the standardization of which is based on determining the markers and not the compounds showing important hypoglycemic function [1].

Polish Pharmacopoeia V, Supplement I [4] states that bean pericarp is pharmacopoeic material used for making two herbal mixtures: species metabolicae (metabolic herbs) and species diureticae (diuretic herbs).

According to Jambor [6], in Poland 10 to 50 tons of bean pericarp are bought and processed and, in respect of the quantity of purchase, is in the same group with Agropyri rhizoma, Chelidonii herba, Arnicae authondium, Origani herba. In spite of many publications [1, 2, 8, 9, 10, 13, 15, 16] concerning the chemical composition and the possibility of using bean pericarp (Phaseoli pericarpium) as medicinal material and the component of many herbal mixtures, there is no research on the comparison and evaluation of the possibility of obtaining this material from bean species cultivated in Poland.

Bean pericarp (Phaseoli pericarpium) as pharmacopoeic material, according to the requirements of Polish Pharmacopoeia VI [5], should contain not less than 0.01% (0.1 mgˇg-1) of phenolic acids in convertion to caffeic acid.

The pericarp of common and runner bean cultivars evaluated in the research was considerably differentiated in respect of the content of free phenolic acids (Table 1). The mean highest content of phenolic acids in convertion to caffeic acid (0.63 mgˇg-1) was found in the pericarp of runner bean, scrub cultivar Eureka, whereas the lowest (0.19 mgˇg-1) in the pericarp of common bean, cultivar Igołomska. The pericarp of runner bean cultivars contained, on average, twice as much of free phenolic acids than the pericarp of common bean cultivars.

Table 1. The content of free phenolic acids in the pericarp of Phaseolus vulgaris L. and Phaseolus coccineus L. in years 1999-2000

Figure 1. Proportional content of identified HPLC free phenolic acids totall in the pericarp of the studied species

The content of free phenolic acids in the pericarp of the examined bean cultivars was considerably differentiated, dependently on the year of the research. The bean pericarp collected in 1999 was distinguishable by considerably higher content of phenolic acids than the one collected in 2000.

In the pericarp of the examined bean cultivars the free phenolic acids identified with HPLC method are as follows: β-resorcylic acid, phydroxybenzoic acid and vanillic acid (Table 2). The participation of particular identified phenolic acids in total in bean pericarp seems to be differentiated and characteristic for the examined bean cultivars. The pericarp of common bean cultivars was characterized by similar content of phydroxybenzoic acid (49%) and vanillic acid (46%) and very low (5%) content of β-resorcylic acid. In the pericarp of runner bean over a half (52%) of total free phenolic acids was vanillic acid and the rest was phydroxybenzoic acid and βresorcylic acid, 24% each (Figure 1).

The content of phenolic acids in convertion to caffeic acid in the pericarp of runner bean cultivars was twice higher (0.47-0.63 mgˇg-1) than in the pericarp of common bean cultivars (0.19-0.30 mgˇg-1). The content of phenolic acids in bean pericarp was considerably changing during the years and exceeded the requirements made for this material.

HPLC examination allowed to determine the presence of phenolic acids, such as βresorcylic acid, phydroxybenzoic acid and vanillic acid in the pericarp of the examined species and cultivars. The participation of particular free phenolic acids in their total in bean pericarp was differentiated and characteristic for the compared species.

The results of the research indicate that the pericarp of runner bean (Phaseolus coccineus L.) may be regarded as herbal material, as it contains valuable biologically active substances. Further research would be advisable in order to estimate the detailed phytochemical composition of the pericarp of this species.

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed Discussions in each series and hyperlinked to the article.